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erfasrc/src/utcut1.c  view on Meta::CPAN

#include "erfa.h"

int eraUtcut1(double utc1, double utc2, double dut1,
              double *ut11, double *ut12)
/*
**  - - - - - - - - - -
**   e r a U t c u t 1
**  - - - - - - - - - -
**
**  Time scale transformation:  Coordinated Universal Time, UTC, to
**  Universal Time, UT1.
**
**  Given:
**     utc1,utc2  double   UTC as a 2-part quasi Julian Date (Notes 1-4)
**     dut1       double   Delta UT1 = UT1-UTC in seconds (Note 5)
**
**  Returned:
**     ut11,ut12  double   UT1 as a 2-part Julian Date (Note 6)
**
**  Returned (function value):
**                int      status: +1 = dubious year (Note 3)
**                                  0 = OK
**                                 -1 = unacceptable date
**
**  Notes:
**
**  1) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
**     convenient way between the two arguments, for example where utc1
**     is the Julian Day Number and utc2 is the fraction of a day.
**
**  2) JD cannot unambiguously represent UTC during a leap second unless
**     special measures are taken.  The convention in the present
**     function is that the JD day represents UTC days whether the
**     length is 86399, 86400 or 86401 SI seconds.
**
**  3) The warning status "dubious year" flags UTCs that predate the
**     introduction of the time scale or that are too far in the future
**     to be trusted.  See eraDat for further details.
**
**  4) The function eraDtf2d converts from calendar date and time of
**     day into 2-part Julian Date, and in the case of UTC implements
**     the leap-second-ambiguity convention described above.
**
**  5) Delta UT1 can be obtained from tabulations provided by the
**     International Earth Rotation and Reference Systems Service.
**     It is the caller's responsibility to supply a dut1 argument
**     containing the UT1-UTC value that matches the given UTC.
**
**  6) The returned ut11,ut12 are such that their sum is the UT1 Julian
**     Date.
**
**  References:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**     Explanatory Supplement to the Astronomical Almanac,
**     P. Kenneth Seidelmann (ed), University Science Books (1992)
**
**  Called:
**     eraJd2cal    JD to Gregorian calendar
**     eraDat       delta(AT) = TAI-UTC
**     eraUtctai    UTC to TAI
**     eraTaiut1    TAI to UT1
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   int iy, im, id, js, jw;
   double w, dat, dta, tai1, tai2;


/* Look up TAI-UTC. */
   if ( eraJd2cal(utc1, utc2, &iy, &im, &id, &w) ) return -1;
   js = eraDat ( iy, im, id, 0.0, &dat);
   if ( js < 0 ) return -1;

/* Form UT1-TAI. */
   dta = dut1 - dat;

/* UTC to TAI to UT1. */
   jw = eraUtctai(utc1, utc2, &tai1, &tai2);
   if ( jw < 0 ) {
      return -1;
   } else if ( jw > 0 ) {
      js = jw;
   }
   if ( eraTaiut1(tai1, tai2, dta, ut11, ut12) ) return -1;

/* Status. */
   return js;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.